兰新铁路百里风区极端风况特征及形成机制

Characteristics and Formation Mechanism of Extreme Wind in Hundred-Li Wind Zone along Lanxin Railway

为揭示兰新铁路百里风区大风的形成机制,利用兰新铁路百里风区及周边5个气象站的日极大风速观测数据,分析百里风区极大风的风速、风向时空分布特征及规律;结合地形地貌,着重分析冷空气爬坡翻山现象及下坡地形的加速作用。百里风区十三间房气象站测到的多年平均日极大风速为18.7m·s^(-1),显著高于百里风区周边其他四站(5.5~9.1m·s^(-1)),且十三间房的盛行风向为北风和北西北风,也显著不同于其他四站。局地气压梯度的增大是形成兰新铁路百里风区大风的根本原因,其具体表现在:1冷空气东移,因受天山山脉东段的阻挡而积聚,使天山山脉的南北气压梯度提高;2在吐鲁番—哈密盆地,地面因日照受热而使热气流上升,与积聚在天山山脉东段的冷空气相遇后,使吐鲁番—哈密盆地与山脉之间的气压增大;3百里风区及其周边特殊的地形加强了由气压梯度所形成大风的风速。

A set of daily extreme wind speed data from five sites in hundred-li wind zone and peripheral areas along the Lanxin Railway in Xinjiang have been analyzed in order to obtain the temporal and spatial distribution characteristics of wind speed and direction of the daily extreme wind and analyze the formation mechanism of gusts in hundred-li wind zone.The upslope wind of cold air and acceleration effects of downslope have been analyzed emphatically combined with topographic features.The main conclusion is that the extreme wind speed is significantly larger at Shisanjianfang,close to the Lanxin Railway,than at any of the other sites and even any other part of the country.Irrespective of direction,the present standard estimates of annual mean value of daily extreme wind speed are 18.7m·s-1 at Shisanjianfang and 5.59.1m·s-1 at the other four sites.Prevail wind direction at Shisanjianfang is N and NNW,also is significantly different from other four sites.In the inner of hundred-li wind zone,prevail wind direction at west of Shisanjianfang is NNE and at the east is NWW.These results are in agreement with those obtained by array of wind eroded hill or hollow.This paper investigates the formation mechanisms for extreme wind that occurs frequently in hundred-li wind zone.The results from climate data analyses and numerical modeling indicate that the extreme wind is primarily a result of a regional-scale pressure gradient that develops due to：1 accumulating of air mass that induced from the passages of cold wave high pressure systems blocked by the Eastern Tianshan Mountains;2 asymmetric heating of the atmosphere between the northern side of the elevated Eastern Tianshan Mountains and the depressed,arid Turpan-Hami Basin on the southern side of hundred-li wind zone;3 the regional terrain relief of Hundred-li wind zone and peripheral areas helps to enhance this pressure gradient and therefore strengthen the flow.This research reveals the formation mechanism of extreme winds in hundred-li wind zone along the Lanxin Railway,and provides the theory support for the windbreak engineering of the Lanxin Railway.